Judges in northern Thailand faced a tough task on Sunday in deciding between more than 750 koi carp at a show dedicated to the colourful fish.

The prized specimens were placed in plastic bags on the floor of the venue in Chiang Mai so they could be scored in various categories including, colour, size and health.

There are more than 100 varieties of koi created through breeding, and each variety is classified into 16 groups.

The largest northern Thailand show of Koi (Carp) decorative fish took place in Chiang Mai, with 750 fish competing for prizes or up for auction. Koi are coloured varieties of Amur Carp and are judged at shows according to their colours, size and health. They command high prices for special features. The highest price ever paid for a Koi was $1.8 million.